Mixtures for producing transparent plastics, transparent plastics, method for producing the same and the use thereof

ABSTRACT

The present invention relates to mixtures for preparing transparent plastics, encompassing
     a) a prepolymer prepared from compounds of the formula (I) and (II)   

     
       
         
         
             
             
         
       
         
          where each R 1 , independently of the others, is hydrogen or a methyl radical, 
          each R 2 , independently of the others, is a linear or branched, aliphatic or cycloaliphatic radical, or a substituted or unsubstituted aromatic or heteroaromatic radical, and each of m and n, independently of the other, is a whole number greater than or equal to 0, where m+n&gt;0, and from compounds of the formula (III), or from alkyl dithiols or from polythiols, preferably
 
HS—R 3 —SH (III)
 
          where R 3 , identical with or different from R 2 , can be as defined for R 2 , and 
         b) at least one monomer (A) capable of free-radical polymerization and having at least 2 methacrylate groups, and 
         c) aromatic vinyl compounds, such as styrene, and 
         d) if appropriate, a monomer capable of free-radical polymerization and having at least two terminal olefinic groups whose reactivity differs, and/or 
         if appropriate, at least one monomer (B) from the group of the methacrylates, preferably 2-hydroxyetyl methacrylate.

The present invention relates to mixtures for preparing transparentplastics. The present invention further relates to transparent plasticswhich can be prepared from the mixtures, and to a process for theirpreparation. The present invention also relates to the use oftransparent plastics for producing optical, especially ophthalmic,lenses.

Spectacles have become an essential component of everyday life. Amongthese, spectacles with plastics lenses have in particular gainedimportance recently, because they weigh less and are less breakable thanspectacle lenses composed of inorganic materials, and can be coloured bymeans of suitable dyes. The production of plastics spectacle lensesgenerally uses high-transparency plastics obtainable, by way of example,from diethylene glycol bis(allyl carbonate) (DAC), thiourethanecompounds having α,ω-terminated multiple bonds or sulphur-containing(meth)acrylates.

DAC plastic has very good impact strength and transparency, and goodprocessibility. However, a disadvantage is that the relatively lowrefractive index n_(D) of about 1.50 requires that both the centre andthe edges of these plastics lenses be reinforced, the spectacle lensesbeing correspondingly thick and heavy. This markedly reduces the wearercomfort of spectacles with DAC plastics lenses.

The specification DE 4234251 discloses sulphur-containingpolymethacrylates which are obtained via free-radical copolymerizationof a monomer mixture composed of compounds of the formula (1) and (2)

Here, Y is an unbranched or branched, acyclic or cyclic alkyl radicalhaving from 2 to 12 carbon atoms, or an aryl radical having from 6 to 14carbon atoms, or an alkaryl radical having from 7 to 20 carbon atoms,and the carbon chains here may have interruption by one or more ether orthioether groups. R is hydrogen or methyl and n is a whole number in therange from 1 to 6.

According to DE 4234251, the monomers of the formula (1) and (2)generally have a molar ratio of from 1:0.5 to 0.5:1. The monomer mixtureis prepared via reaction of at least two mols of (meth)acryloyl chlorideor (meth)acrylic anhydride with one mole of a dithiol, by reacting the(meth)acryloyl chloride or (meth)acrylic anhydride in an inert organicsolvent and the dithiol in aqueous alkaline solution. Suitable solventsmentioned are methyl tert-butyl ether, toluene and xylene, thedielectric constant of these at 20° C. being 2.6, 2.4 and, respectively,from 2.3 to 2.6.

The plastics described in DE 4234251 are colourless, rigid and slightlybrittle and have a high refractive index n_(D) in the range from 1.602to 1.608. The Abbe number is from 35 to 38. These plastics too,therefore, have only limited suitability for spectacle lenses. Again,this specification gives no information concerning the glass transitiontemperature of the plastics.

The specification WO 03/011925 describes the polymerization ofthiomethacrylates with polyethylene glycol derivatives. The resultantplastics may be used, inter alia, for producing optical lenses. Adisadvantage of these lenses is their mechanical properties. Inparticular, for example, impact strength is insufficient for manyrequirements.

In the light of the prior art, it was then an object of the presentinvention to provide mixtures for preparing transparent plastics whichare suitable as a material for optical lenses, where the plastics haveideal mechanical properties, in particular high impact strength,together with a high refractive index, preferably greater than 1.59, anda maximum Abbe number, preferably greater than 36. In particular, itshould be possible to produce plastics spectacle lenses which have a lowlevel of dispersion and no colouring at the edges.

The present invention was also based on the object of providing astarting material composition for preparing a high-transparency plasticwith improved mechanical properties, even at temperatures above roomtemperature. In particular, the glass transition temperature of theinventive plastic should be maximized, preferably being above 80.0° C.

It was therefore an object of the present invention to provide ahigh-transparency plastic which can be prepared from the startingmaterial composition in a simple manner, on an industrial scale and atlow cost. In particular, it should be obtainable via free-radicalpolymerization from a mixture which is flowable at atmospheric pressureand temperatures in the range from 20.0 to 80.0° C.

Another object on which the present invention was based was to provideapplication sectors and possible uses for the inventivehigh-transparency plastic.

A mixture with all of the features of Patent claim 1 achieves theseobjects, and also achieves other objects which, although not explicitlymentioned, are readily derivable or deducible from the circumstancesdiscussed in the introduction. Advantageous modifications of theinventive mixture are protected in the subclaims dependent on claim 1.Other subject matters claimed are the high-transparency plasticsobtainable from the inventive mixtures, and also a process for theirpreparation. The use claim protects a preferred use of the inventivehigh-transparency plastic. Another product claim describes an optical,preferably ophthalmic, lens which comprises the inventivehigh-transparency plastic.

Mixtures Encompassing

-   a) a prepolymer prepared from compounds of the formula (I) and (II)

-    where each R¹, independently of the others, is hydrogen or a methyl    radical, each R², independently of the others, is a linear or    branched, aliphatic or cycloaliphatic radical, or a substituted or    unsubstituted aromatic or heteroaromatic radical, and each of m and    n, independently of the other, is a whole number greater than or    equal to 0, where m+n>0, and from alkyl dithiols or from polythiols,    preferably compounds of the formula (III)    HS—R³—SH (III)    where R³ can be identical or different from the definition given for    R²-   b) at least one monomer (A) capable of free-radical polymerization    and having at least 2 methacrylate groups, and-   c) aromatic vinyl compounds,    which are suitable for preparing transparent plastics, and which    have excellent mechanical and optical properties. The mixtures may,    if appropriate, comprise-   d) a monomer capable of free-radical polymerization and having at    least two terminal olefinic groups whose reactivity differs, for    example a bifunctional monomer having a methacrylate end group and a    vinyl end group, and/or-   e) at least one ethylenically unsaturated monomer (B), preferably    from the group of the methacrylates, particularly preferably    2-hydroxyethyl methacrylate.

The inventive transparent plastic has a previously unknown combinationof exceptional properties, such as high refractive index, high Abbenumber, good impact strength, and also high glass transitiontemperature. The corresponding plastics spectacle lenses have a lowlevel of dispersion; no colouring at the edges is observed.

The inventive transparent plastic also has further advantages. Amongthese are:

-   Since the inventive plastic has high refractive index, there is no    requirement for reinforcement and therefore thickening of the centre    and of the edges of corresponding plastics spectacle lenses, and    there is a marked increase in the wearer comfort provided by these    spectacles, due to the comparatively low weight.-   The very good impact strength of the inventive plastic protects the    corresponding plastics spectacle lenses from the “risks of everyday    life”. In particular in the case of thin spectacle lenses, it is    very unlikely that mechanical forces will cause impairment or    irreparable damage.-   The glass transition temperature of the inventive high-transparency    plastic is high, preferably above 80.0° C., and up to this    temperature the plastic therefore retains its exceptional mechanical    properties, in particular high impact strength, and its hardness.-   The inventive high-transparency plastic can be prepared via    free-radical copolymerization in a simple manner, on an industrial    scale, at low cost, of a monomer mixture which is preferably    flowable at atmospheric pressure and temperatures in the range from    20.0 to 80.0° C.-   The underlying monomer mixture can likewise be prepared in a simple    manner, on an industrial scale, and at low cost.

The prepolymer of the present invention encompasses compounds of theformula (I) and/or (II) and (III)

where each R¹, independently of the others, is hydrogen or a methylradical, preferably a methyl radical, and each R², independently of theothers, is a linear or branched, aliphatic or cycloaliphatic radical, ora substituted or unsubstituted aromatic or heteroaromatic radical, wherethe radical R² may preferably encompass from 1 to 100, in particularfrom 1 to 20, carbon atoms and each radical R³, irrespective of R², is alinear or branched, aliphatic or cycloaliphatic radical or a substitutedor unsubstituted aromatic or heteroaromatic radical, where the radicalR³ can preferably encompass from 1 to 100, in particular from 1 to 20,carbon atoms.

By way of example, among the preferred linear or branched, aliphatic orcycloaliphatic radicals are the methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene, or cyclohexylenegroup.

Among the preferred divalent aromatic or heteroaromatic radicals are inparticular groups which derive from benzene, from naphthalene, frombiphenyl, from diphenyl ether, from diphenylmethane, fromdiphenyldimethyl-methane, from bisphenone, from diphenyl sulphone, fromquinoline, from pyridine, from anthracene, and from phenanthrene. Forthe purposes of the present invention, cycloaliphatic radicals here alsoencompass bi-, tri- and polycyclic aliphatic radicals.

The radical R² or R³ also encompasses radicals of the formula

where each R⁴, independently of the others, is a linear or branched,aliphatic or cycloaliphatic radical, e.g. a methylene, ethylene,propylene, isopropylene, n-butylene, isobutylene, tert-butylene orcyclohexylene group. Each radical X, independently of the others, isoxygen or sulphur, and the radical R⁵ is a linear or branched, aliphaticor cycloaliphatic radical, e.g. a methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene or cyclohexylenegroup. For the purposes of the present invention, cycloaliphaticradicals here also encompass bi-, tri- and polycyclic aliphaticradicals. Y is a whole number from 1 to 10, in particular 1, 2, 3 or 4.

Preferred Radicals of the Formula (Ia) Encompass:

The radical R² is preferably an aliphatic radical having from 1 to 10carbon atoms, preferably a linear aliphatic radical having from 2 to 8carbon atoms. Each of the indices m and n, independently of the others,is a whole number greater than or equal to 0, such as 0, 1, 2, 3, 4, 5or 6. The sum m+n here is greater than 0, preferably in the range from 1to 6, advantageously in the range from 1 to 4, in particular 1, 2 or 3.

To prepare the prepolymer, each of the compounds of the formula (I) and(II), and also each of the compounds of the formula (III), may be usedindividually or else in the form of a mixture of two or more compoundsof the formula (I), (II) and, respectively, (III).

The relative proportions of the compounds of the formula (I), (II) and(III) in the inventive monomer mixture may in principle be as desired,and they can be utilized to “tailor” the property profile of theinventive plastic to the demands of the application. By way of example,it can be extremely advantageous for the monomer mixture to comprise amarked excess of compound(s) of the formula (I) or compound(s) of theformula (II) or compound(s) of the formula (III), based in each case onthe total amount of compounds of the formula (I), (II) and (III) in theprepolymer.

However, for the purposes of the present invention it is particularlyadvantageous for the mixture to comprise more than 10 mol %, preferablymore than 12 mol %, in particular more than 14 mol %, based on the totalamount of the compounds of the formula (I) and (II), of compounds of theformula (II) where m+n=2. If R² is an ethylene radical, the proportionby weight of (II) where m+n=2 in the mixture is more than 10%, inparticular more than 15%.

It is moreover particularly advantageous according to the invention touse mixtures which comprise more than 5.8 mol %, advantageously morethan 6.5 mol %, in particular more than 7.5 mol %, based on the totalamount of the compounds of the formula (I) and (II), of compounds of theformula (II) where m+n=3. This corresponds to a proportion by weight of(II) of at least 6% if R² is an ethylene radical, where m+n=3.

The proportion of the compounds (I) is preferably from 0.1 to 50.0 mol%, advantageously from 10.0 to 45.0 mol %, in particular from 20.0 to35.0 mol %, based on the total amount of the compounds of the formula(I) and (II), corresponding to a preferred range for the preparation byweight of the compound (I) of from 15 to 40% if R² is an ethyleneradical. The proportion of the compounds (II) where m+n=1 is preferablyfrom 1 to 40.0 mol %, advantageously from 5 to 35.0 mol %, in particularfrom 10 to 30 mol %, based on the total amount of the compounds of theformula (I) and (II). This corresponds to a preferred proportion byweight of the compounds (II) where m+n=1 of from 10 to 45% if R² is anethylene radical. The proportion of the compounds (II) where m+n>3 ispreferably greater than 0 mol %, advantageously greater than 1 mol %, inparticular greater than 2 mol %, based on the total amount of thecompounds of the formula (I) and (II). If R² is an ethylene radical, theproportion by weight for compounds (II) where m+n>3 in the mixture ismore than 2%, in particular more than 5%.

The proportion of the compounds (III) in the prepolymer is preferablyfrom 1 to 55.0 mol %, in particular from 10.0 to 50.0 mol %, based onthe total amount of the compounds of the formula (I), (II) and (III).If, in a specific case, R³ is a dimercaptodioxaoctane radical, then theproportion by weight of (III) in the prepolymer, based on the totalamount of the compounds (I), (II) and (III) is more than 0.5%,preferably more than 5%.

Processes for preparing the compounds of the formula (I) and (II) areknown to the person skilled in the art, for example from DE 4234251, thedisclosure of which is expressly incorporated herein by way ofreference. However, for the purposes of the present invention, it hasproven very particularly advantageous to prepare a mixture of thecompounds of the formula (I) and (II) via a process in which from 1.0 to<2.0 mol, preferably from 1.1 to 1.8 mol, advantageously from 1.2 to 1.6mol, in particular from 1.2 to 1.5 mol, of at least one compound of theformula (IV)

are reacted with one mole of at least one polythiol of the formula (V)

The radical X is halogen, in particular chlorine or bromine, or aradical

this means that the compounds of the formula (IV) encompass, inter alia,acryloyl chloride, methacryloyl chloride, acrylic anhydride andmethacrylic anhydride, particular preference being given to the use ofacrylic anhydride, methacrylic anhydride or mixtures of the two.

Each M indicates, independently of the other, hydrogen or a metalcation. Preferred metal cations derive from elements whoseelectronegativity is smaller than 2.0, advantageously smaller than 1.5,particular preference being given to alkali metal cations, in particularNa⁺, K⁺, Rb⁺, Cs⁺ and alkaline earth metal cations, in particular Mg²⁺,Ca²⁺, Sr²⁺, Ba²⁺. Very particularly advantageous results may be achievedusing the metal cations Na³⁰ and K³⁰ .

Polythiols of the formula (V) particularly suitable in this contextencompass 1,2-ethanedithiol, 1,2-propane dithiol, 1,3-propanedithiol,1,2-butanedithiol, 1,3-butanedithiol, 1,4-butanedithiol,2-methylpropane-1,2-dithiol, 2-methylpropane-1,3-dithiol,3,6-dioxa-1,8-octanedithiol (dimercaptodioxaoctane=DMDO),ethylcyclohexyl dimercaptans obtainable via reaction of4-ethenylcyclohexene with hydrogen sulphite,ortho-bis(mercaptomethyl)benzene, meta-bis(mercaptomethyl)benzene,para-bis(mercaptomethyl)-benzene, compounds of the formula (V)

and also compounds of the formula

where each R⁴, independently of the others, is a linear or branched,aliphatic or cycloaliphatic radical, such as a methylene, ethylene,propylene, isopropylene, n-butylene, isobutylene, tert-butylene orcyclohexylene group. For the purposes of the present invention,cycloaliphatic radicals here also encompass bi-, tri- and polycyclicaliphatic radicals. Each radical X, independently of the others, isoxygen or sulphur, and the radical R⁵ is a linear or branched, aliphaticor cycloaliphatic radical, such as a methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene or cyclohexylenegroup. For the purposes of the present invention, cycloaliphaticradicals here also encompass bi-, tri- and polycyclic aliphaticradicals. y is a whole number from 1 to 10, in particular 1, 2, 3 or 4.

Preferred compounds of the formula (Va) encompass:

For the purposes of one particularly preferred embodiment of thisprocess, the compound used of the formula (V) comprises1,2-ethanedithiol.

This process reacts the compound(s) of the formula (IV) in at least oneinert, organic solvent S, and the compound(s) of the formula (V) inaqueous alkaline solution, the expression “inert, organic solvent”applying to organic solvents which do not react with the compoundspresent in the reaction system under the respective reaction conditions.

It is preferable for at least one solvent S to have a relativedielectric constant >2.6, preferably >3.0, advantageously >4.0, inparticular >5.0, in each case measured at 20° C. In this context, therelative dielectric constant indicates a dimensionless value stating thefactor by which the capacitance C of a (theoretical) capacitor locatedwithin a vacuum increases when substances with dielectric properties,known as dielectrics, are introduced between the plates. This value ismeasured at 20° C. and extrapolated to low frequencies (ω→0). Forfurther details reference is made to the familiar technical literature,in particular to Ullmann Encyklopädie der technischen Chemie, [Ullmann'sEncyclopaedia of Industrial Chemistry] Volume 2/1 Anwendungphysikalischer und physikalisch-chemischer Methoden im Laboratorium[Application of physical and physico-chemical methods in thelaboratory], headword: Dielektrizitätskonstante [Dielectric constant],pp. 455-479. Dielectric values of solvents are given, inter alia, inHandbook of Chemistry and Physics, 71st edition, CRC Press, Baco Raton,Ann Arbor, Boston, 1990-1991, pp. 8-44, 8-46 and 9-9 to 9-12.

For the purposes of this process it is moreover particularlyadvantageous for the solvent and the aqueous solution to form two phasesduring the reaction and not to be capable of homogeneous mixing. To thisend, the water solubility value for the solvent, measured at 20° C., ispreferably smaller than 10 g of water, based on 100 g of solvent.

Solvents S preferred according to the invention encompass

-   aliphatic ethers, such as diethyl ether (4.335), dipropyl ether,    diisopropyl ether;-   cycloaliphatic ethers, such as tetrahydrofuran (7.6);-   aliphatic esters, such as methyl formate (8.5), ethyl formate,    propyl formate, methyl acetate, ethyl acetate, n-butyl acetate    (5.01), methyl propionate, methyl butyrate (5.6), ethyl butyrate,    2-methoxyethyl acetate;-   aromatic esters, such as benzyl acetate, dimethyl phthalate, methyl    benzoate (6.59), ethyl benzoate (6.02), methyl salicylate, ethyl    salicylate, phenyl acetate (5.23);-   aliphatic ketones, such as acetone, methyl ethyl ketone (18.5),    2-pentanone (15.4), 3-pentanone (17.0), methyl isoamyl ketone,    methyl isobutyl ketone (13.1);-   aromatic ketones, such as acetophenone;-   nitroaromatics, such as nitrobenzene, o-nitrotoluene (27.4),    m-nitrotoluene (23), p-nitrotoluene;-   halogenated aromatics, such as chlorobenzene (5.708),    o-chlorotoluene (4.45), m-chlorotoluene (5.55), p-chlorotoluene    (6.08), o-dichlorobenzene, m-dichlorobenzene; heteroaromatics, such    as pyridine, 2-methylpyridine (9.8), quinoline, isoquinoline; and    mixtures of these compounds, the data in brackets being the    respective associated relative dielectric constants at 20° C.

Compounds very particularly suitable here for the purposes of thepresent invention are aliphatic esters and cycloaliphatic ethers, inparticular ethyl acetate and tetrahydrofuran.

For the purposes of the present process, it is possible either to usethe solvent S alone or else to use a solvent mixture, in which case itis not necessary that all of the solvents present in the mixture complywith the abovementioned dielectric criterion. By way of example,according to the invention it is also possible to usetetrahydrofuran/cyclohexane mixtures. However, it has provenadvantageous for the solvent mixture to have a relative dielectricconstant >2.6, preferably >3.0, advantageously >4.0, in particular >5.0,in each case measured at 20° C. Particularly advantageous results can beachieved using solvent mixtures which comprise only solvents whoserelative dielectric constant is >2.6, preferably >3.0,advantageously >4.0, in particular >5.0, in each case measured at 20° C.

The aqueous alkaline solution of the compound(s) of the formula (V)preferably comprises from 1.1 to 1.5 val (equivalents) of at least oneBronsted base, based on the total amount of compound(s) of the formula(IV). Preferred Bronsted bases for the purposes of the present inventionencompass alkali metal hydroxides and alkaline earth metal hydroxides,in particular sodium hydroxide and potassium hydroxide.

In principle, any conceivable method may be used for the conduct of thereaction. By way of example, the compound(s) of the formula (IV) mayform an initial charge in the solvent (mixture) S, and the aqueousalkaline solution of the compound(s) of the formula (V) may be addedstepwise or continuously. However, for the purposes of the presentinvention it has proven very particularly advantageous to meter thecompound(s) of the formula (IV) in at least one inert, organic solvent Sand the compound(s) of the formula (V) in aqueous alkaline solution tothe reaction vessel in parallel.

The reaction temperature may be varied widely, but the temperature isoften in the range from 20.0 to 120.0° C., preferably in the range from20.0 to 80.0° C. Similar considerations apply for the pressure at whichthe reaction is completed. The reaction may therefore take place eitherat subatmospheric pressure or else at superatmospheric pressure.However, it is preferably carried out at atmospheric pressure. Althoughthe reaction can also take place in air, it has proven very particularlyadvantageous for the purposes of the present invention to carry out thereaction under an inert gas, preferably nitrogen and/or argon,preferably with a very small proportion of oxygen present.

The reaction mixture is advantageously reacted in a further step with aBronsted acid, preferably until the pH of the aqueous solution at 20° C.is below 7.0, advantageously below 6.0, in particular below 5.0. Acidswhich may be used in this context encompass inorganic mineral acids,such as hydrochloric acid, sulphuric acid, phosphoric acid, organicacids, such as acetic acid, propionic acid, and acidic ion exchangers,in particular acidic synthetic resin ion exchangers, e.g. ®Dowex M-31(H). The method which has proven very particularly successful here isthe use of acidic synthetic resin ion exchangers loaded with at least1.0 meq, preferably at least 2.0 meq, in particular at least 4.0 meq, ofH⁺ ions, based on 1 g of dry ion exchanger, grain sizes of from 10 to 50mesh and porosities in the range from 10 to 50%, based on the totalvolume of the ion exchanger.

In an advantageous method for isolating the compounds of the formula (I)and (II) the organic phase composed of the solvent S is separated offand, where appropriate, washed, and dried, and the solvent isevaporated.

During the reaction of the compound(s) of the formula (IV) with thecompound(s) of the formula (V) it is possible to add inhibitors whichinhibit free-radical polymerization of the (meth)acrylic groups duringthe reaction. These inhibitors are well-known to persons skilled in theart.

Use is mainly made of 1,4-dihydroxybenzenes. However, it is alsopossible to use dihydroxybenzenes having other substitution. Theseinhibitors can generally be represented by the general formula (VI)

where

-   R⁶ is a linear or branched alkyl radical having from one to eight    carbon atoms, halogen or aryl, preferably an alkyl radical having    from one to four carbon atoms, particularly preferably methyl,    ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl,    tert-butyl, Cl, F or Br;-   o is a whole number in the range from one to four, preferably one or    two; and-   R⁷ is hydrogen, a linear or branched alkyl radical having from one    to eight carbon atoms, or aryl, preferably an alkyl radical having    from one to four carbon atoms, particularly preferably methyl,    ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or    tert-butyl.

However, it is also possible to use compounds whose parent compound is1,4-benzoquinone. These may be described by the formula (VII)

where

-   R⁶ and o are as defined above.

Use is also made of phenols of the general structure (VIII)

where

-   R⁸ is a linear or branched alkyl radical having from one to eight    carbon atoms, aryl or aralkyl, propionic esters with mono- to    tetrahydric alcohols, which may also contain heteroatoms, such as S,    O and N, preferably an alkyl radical having from 1 to 4 carbon    atoms, particularly preferably methyl, ethyl, n-propyl, isopropyl,    n-butyl, isobutyl, sec-butyl, tert-butyl.

Another advantageous class of substance is represented by hinderedphenols based on triazine derivatives of the formula (IX)

-   where R⁹ =a grouping of the formula (X)

-    where-   R¹⁰=C_(p)H_(2p+1)-   where p=1 or 2.

Compounds used with particular success are 1,4-dihydroxybenzene,4-methoxyphenol, 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone,1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,2,6-di-tert-butyl-4-methylphenol, 2,4-dimethyl-6-tert-butylphenol,2,2-bis[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl-1-oxopropoxymethyl)]1,3-propanediylester, 2,2′-thiodiethylbis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate,3,5-bis(1,1-dimethylethyl-2,2′-methylenebis(4-methyl-6-tert-butyl)phenol,tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-s-triazine-2,4,6-(1H,3H,5H)trione,tris(3,5-di-tert-butyl-4-hydroxy)-s-triazine-2,4,6-(1H,3H,5H)trione ortert-butyl-3,5-dihydroxybenzene.

Based on the weight of the entire reaction mixture, the proportion ofthe inhibitors individually or in the form of a mixture is generallyfrom 0.01 to 0.50% (by weight), the concentration of the inhibitorspreferably being selected in such a way as not to impair the DIN 55945colour number. Many of these inhibitors are commercially available.

For the purposes of the present invention, the mixture also comprises,alongside the prepolymer, prepared from compounds of the formula (I),(II) and (III), at least one monomer (A) capable of free-radicalpolymerization and having at least two terminal methacrylate groups.

Examples of these di(meth)acrylates are polyoxymethylene-(meth)acrylicacid derivatives and polyoxypropylene-(meth)acrylic acid derivatives,e.g. triethylene glycol (meth)acrylate, tetraethylene glycol(meth)acrylate, tetrapropylene glycol (meth)acrylate, and also1,4-butanediol di(meth)acrylate, diethylene glycol di(meth)acrylate,dipropylene glycol di(meth)acrylate, triethylene glycoldi(meth)acrylate, tripropylene glycol di(meth)acrylate. Tetraethyleneglycol di(meth)acrylate, tetrapropylene glycol di(meth)acrylate,polyethylene glycol di (meth) acrylate (preferably having weight-averagemolar masses in the range from 200 to 5 000 000 g/mol, advantageously inthe range from 200 to 25 000 g/mol, in particular in the range from 200to 1000 g/mol), polypropylene glycol di(meth)acrylate (preferably withweight-average molar masses in the range from 200 to 5 000 000 g/mol,advantageously in the range from 250 to 4000 g/mol, in particular in therange from 250 to 1000 g/mol), 2,2′-thiodiethanol di(meth)acrylate(thiodiglycol di(meth)acrylate),

-   3,9-di(meth)acryloyloxymethyltricyclo[5.2.1.0(2.6)]-decane, in    particular

-   3,8-di(meth)acryloyloymethyltricyclo[5.2.1.0(2.6)]-decane-   4,8-di(meth)acryloyloymethyltricyclo[5.2.1.0(2.6)]-decane,-   4,9-di(meth)acryloyloymethyltricyclo[5.2.1.0(2.6)]-decane,    ethoxylated bisphenol A di(meth)acrylate, in particular

-   where s and t are greater than or equal to zero, and the sum of s    and t is preferably in the range from 1 to 30, in particular in the    range from 2 to 10, and di(meth)acrylates obtainable via reaction of    diisocyanates with 2 equivalents of hydroxyalkyl (meth)acrylate, in    particular

-   where each radical R¹¹, independently of the others, is hydrogen or    a methyl radical,-   tri(meth)acrylates, such as trimethylolpropane tri(meth)acrylate and    glycerol tri(meth)acrylate, or else (meth)acrylates of ethoxylated    or propoxylated glycerol, of trimethylolpropane, or of other    alcohols having more than 2 hydroxy groups.-   Di(meth)acrylates of the formula (XI) have proven particularly    successful as monomer (A).

Each R¹² here, independently of the others, is hydrogen or methyl. R¹³indicates a linear or branched alkyl or cycloalkyl radical, or anaromatic radical preferably having from 1 to 100, with preference from 1to 40, preferably from 1 to 20, advantageously from 1 to 8, inparticular from 1 to 6, carbon atoms, e.g. a methyl, ethyl, propyl,isopropyl, n-butyl, isobutyl, tert-butyl, cyclopentyl, cyclohexyl, orphenyl group. For the purposes of the present invention, cycloaliphaticradicals here also encompass bi-, tri-, and polycyclic aliphaticradicals. Linear or branched alkyl or cycloalkyl radicals having from 1to 6 carbon atoms are very particularly preferred as R¹⁸.

The radical R¹³ is preferably a linear or branched, aliphatic orcycloaliphatic radical, such as a methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene or cyclohexylenegroup, or a radical of the general formula

where the radical R¹⁵ is a linear or branched, aliphatic orcycloaliphatic radical, or a substituted or unsubstituted aromatic orheteroaromatic radical, e.g. a methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene or cyclohexylenegroup, or divalent aromatic or heteroaromatic groups which derive frombenzene, from naphthalene, from biphenyl, from diphenyl ether, fromdiphenylmethane, from diphenyldimethylmethane, from bisphenone, fromdiphenyl sulphone, from quinoline, from pyridine, from anthracene, orfrom phenanthrene. For the purposes of the present invention,cycloaliphatic radicals here also encompass bi-, tri- and polycyclicaliphatic radicals. Each radical R¹⁴, independently of the others, is alinear or branched, aliphatic or cycloaliphatic radical or a substitutedor unsubstituted aromatic or heteroaromatic radical, e.g. a methylene,ethylene, propylene, isopropylene, n-butylene, isobutylene,tert-butylene or cyclohexylene group, or divalent aromatic orheteroaromatic groups which derive from benzene, from naphthalene, frombiphenyl, from diphenyl ether, from diphenylmethane, fromdiphenyldimethylmethane, from bisphenone, from diphenyl sulphone, fromquinoline, from pyridine, from anthracene, or from phenanthrene. For thepurposes of the present invention, cycloaliphatic radicals here alsoencompass bi-, tri- and polycyclic aliphatic radicals. Each radicalX^(I), independently of the others, is oxygen, sulphur, an ester groupof the general formula (XIb), (XIc),

-   a urethane group of the general formula (XId), (XIe), (XIf) or    (XIg),

-    a thiourethane group of the general formula (XIh), (XIi), (XIj) or    (XIk),

-    a dithiourethane group of the general formula (XIl), (XIm), (XIn)    or (XIo)

-    or a thiocarbamate group of the general formula (XIp), (XIq), (XIr)    or (XIs)

preferably oxygen, where the radical R¹⁶ is a linear or branched,aliphatic or cycloaliphatic radical or a substituted or unsubstitutedaromatic or heteroaromatic radical, e.g. a methyl, ethyl, propyl,isopropyl, n-butyl, isobutyl, tert-butyl or cyclohexyl group, ormonovalent aromatic or heteroaromatic groups derived from benzene, fromnaphthalene, from biphenyl, from diphenyl ether, from diphenylmethane,from diphenyldimethylmethane, from bisphenone, from diphenyl sulphone,from quinoline, from pyridine, from anthracene, or from phenanthrene.For the purposes of the present invention, cycloaliphatic radicals herealso encompass bi-, tri- and polycyclic aliphatic radicals. z is a wholenumber from 1 to 1000, advantageously from 1 to 100, in particular from1 to 25.

Particularly preferred di(meth)acrylates of the formula (XI) encompassethylene glycol di(meth)acrylate, ethoxylated bisphenol Adi(meth)acrylate, in particular

where s and t are greater than or equal to zero and the sum of s and tis preferably in the range from 1 to 20, in particular in the range from2 to 10, and di(meth)acrylates obtainable via reaction of diisocyanateswith 2 equivalents of hydroxyalkyl (meth)acrylate, in particular

where each radical R¹⁷, independently of the others, is hydrogen or amethyl radical,

-   3,8-di(meth)acryloyloxymethyltricyclo[5.2.1.0(2.6)]-decane,-   3,9-di(meth)acryloyloxymethyltricyclo[5.2.1.0(2.6)]-decane,-   4,8-di(meth)acryloyloxymethyltricyclo[5.2.1.0(2.6)]-decane,-   4,9-di(meth)acryloyloxymethyltricyclo[5.2.1.0(2.6)]-decane,    thiodiglycol di(meth)acrylate, polypropylene glycol    di(meth)acrylate, preferably with a weight-average molar mass in the    range from 200 to 1000 g/mol, and/or polyethylene glycol    di(meth)acrylate, preferably with a weight-average molar mass in the    range from 200 to 1000 g/mol. Particular preference is given here to    the dimethacrylates of the compounds mentioned. Very particularly    advantageous results are achieved using polyethylene glycol    dimethacrylate, preferably with a weight-average molar mass in the    range from 200 to 1000 g/mol.

The proportion of monomer (A) is from 2 to 50% by weight, in particularfrom 10 to 30% by weight, based on all of the monomers used in themixture.

For the purposes of the present invention, the mixture also comprises,alongside the prepolymer composed of the compounds of the formula (I),(II), and (III), and at least one monomer (A) capable of free-radicalpolymerization, an aromatic vinyl compound.

Among the aromatic vinyl compounds, preference is given to the use ofstyrenes, substituted styrenes having an alkyl substituent in the sidechain, e.g. α-methylstyrene and α-ethylstyrene, substituted styreneshaving an alkyl substituent on the ring, e.g. vinyltoluene andp-methylstyrene, halogenated styrenes, such as monochlorostyrenes,dichlorostyrenes, tribromostyrenes, and tetrabromostyrenes,

and also to dienes, such as 1,2-divinylbenzene, 1,3-divinylbenzene,1,4-divinylbenzene, 1,2-diisopropenylbenzene, 1,3-diisopropenylbenzene,and 1,4-diisopropenylbenzene.

The proportion of the aromatic vinyl compounds is from 5 to 40% byweight, preferably from 10 to 30% by weight, particularly preferablyfrom 15 to 25% by weight, based on the total amount of the compounds ofthe formula (I), (II), and (III) used in the prepolymer, the monomer (A)capable of free-radical polymerization, and the aromatic vinyl compoundsand other monomers optionally used.

Surprisingly, the addition of monomer (A) and the aromatic vinylcompound improves the mechanical properties of the inventive plasticsmaterial without adversely affecting its optical properties. In manyinstances, a favourable effect on optical properties is found.

According to one particular aspect of the present invention, compounds,preferably molecules having a linear structure and varying chain lengths(asymmetric crosslinking agents) of the general formula (XII) may bepresent

where the radical R¹⁹ is independently a hydrogen atom, a fluorine atomand/or a methyl group, the radical R¹⁸ is a connecting group, preferablyencompassing from 1 to 1000, in particular from 2 to 100, carbon atomsand the radical Y is a bond or a connecting group having from 0 to 1000carbon atoms, in particular from 1 to 1000 carbon atoms, and preferablyfrom 1 to 100 carbon atoms. The length of the molecule can be varied byway of the molecular component R¹⁸. Compounds of the formula (XII) have,at one end of the molecule, a terminal (meth)acrylate function, and atthe other end have a terminal group other than a methacrylate function.Among the preferred groups Y are in particular a bond (vinyl group), aCH₂ group (allyl group), and also aliphatic or aromatic groups havingfrom 1 to 20 carbon atoms, for example a benzene-derived group, thealiphatic or aromatic groups particularly preferably containing aurethane group.

The radical R¹⁸ is preferably a linear or branched, aliphatic orcycloaliphatic radical, such as a methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene or cyclohexylenegroup, or a radical of the general formula

where the radical R²¹ is a linear or branched, aliphatic orcycloaliphatic radical or a substituted or unsubstituted aromatic orheteroaromatic radical, e.g. a methylene, ethylene, propylene,isopropylene, n-butylene, isobutylene, tert-butylene or cyclohexylenegroup, or divalent aromatic or heteroaromatic groups which derive frombenzene, from naphthalene, from biphenyl, from diphenyl ether, fromdiphenylmethane, from diphenyldimethylmethane, from bispheonone, fromdiphenyl sulphone, from quinoline, from pyridine, from anthracene orfrom phenanthrene. For the purposes of the present invention,cycloaliphatic radicals here also encompass bi-, tri- and polycyclicaliphatic radicals. Each radical R²⁰ here, independently of the others,is a linear or branched, aliphatic or cycloaliphatic radical or asubstituted or unsubstituted aromatic or heteroaromatic radical, e.g. amethylene, ethylene, propylene, isopropylene, n-butylene, isobutylene,tert-butylene or cyclohexylene group, or divalent aromatic orheteroaromatic groups which derive from benzene, from naphthalene, frombiphenyl, from diphenyl ether, from diphenylmethane, fromdiphenyldimethylmethane, from bisphenone, from diphenyl sulphone, fromquinoline, from pyridine, from anthracene or from phenanthrene. For thepurposes of the present invention, cycloaliphatic radicals here alsoencompass bi-, tri- and polycyclic aliphatic radicals. Each radical X¹,independently of the others, is oxygen, sulphur, an ester group of thegeneral formula (XIIb), (XIIc),

a urethane group of the general formula (XIId), (XIIe), (XIIf) or(XIIg),

a thiourethane group of the general formula (XIIh), (XIIi), (XIIj) or(XIIk),

a dithiourethane group of the general formula (XIIl), (XIIm), (XIIn) or(XIIo)

or a thiocarbamate group of the general formula (XIIp), (XIIq), (XIIr)or (XIIs)

preferably oxygen, where the radical R²² is a linear or branched,aliphatic or cycloaliphatic radical or a substituted or unsubstitutedaromatic or heteroaromatic radical, e.g. a methyl, ethyl, propyl,isopropyl, n-butyl, isobutyl, tert-butyl or cyclohexyl group, ormonovalent aromatic or heteroaromatic groups derived from benzene, fromnaphthalene, from biphenyl, from diphenyl ether, from diphenylmethane,from diphenyldimethylmethane, from bisphenone, from diphenyl sulphone,from quinoline, from pyridine, from anthracene, or from phenanthrene.For the purposes of the present invention, cycloaliphatic radicals herealso encompass bi-, tri- and polycyclic aliphatic radicals. z is a wholenumber from 1 to 1000, advantageously from 1 to 100, in particular from1 to 25.

In one particular embodiment of the formula (XII) the compounds comprisethose of the formula (XIII)

and/or of the formula (XIV),

where each of the radicals R²³ and R²⁴, independently of the other, ishydrogen or a methyl radical, and the radical R²⁵ is a linear orbranched, aliphatic or cycloaliphatic divalent radical, or a substitutedor unsubstituted aromatic or heteroaromatic divalent radical. Preferredradicals have been described above.

The length of the chain may be influenced via variation of the number ofpolyalkylene oxide units, preferably polyethylene glycol units.Compounds of the formula (XIII) and (XIV) which have proven particularlysuitable for the method described here of achieving the object havenumbers of polyoxyalkylene oxide units r, p and q which are,independently of the others, from 1 to 40, preferably from 5 to 20, inparticular from 7 to 15 and particularly preferably from 8 to 12.

Asymmetric crosslinking agents which are very particularly preferredaccording to the invention encompass compounds of the formula (XIV), inparticular

where s and t are greater than or equal to zero and the sum s+t ispreferably in the range from 1 to 20, in particular in the range from 2to 10, and compounds of the formula (XIII), in particular

where t is greater than or equal to zero and t is preferably in therange from 1 to 20, in particular in the range from 2 to 10.

According to one particular aspect, the mixture preferably comprisesfrom 0.5 to 40% by weight, in particular from 5 to 15% by weight, ofcompounds of the formula (XII) and/or (XIII), based on the total weightof the monomer mixture.

For the purposes of one particularly preferred embodiment of the presentinvention, the inventive mixture also comprises at least oneethylenically unsaturated monomer (B). These monomers (B) differ fromthe asymmetric compounds of the formulae (XIII) and (XIV), and from themonomers (A) and the thio(meth)acrylates of the formulae (I) and/or(II). The monomers (B) are known to persons skilled in the art and arepreferably copolymerizable with the monomers (A) and thethio(meth)acrylates of the formulae (I) and/or (II). Among thesemonomers (B) are in particular

-   nitriles of (meth)acrylic acid and other nitrogen-containing    methacrylates, such as methacryloylamidoacetonitrile,    2-methacryloyloxyethylmethylcyanamide, cyanomethyl methacrylate;-   (meth)acrylates which derive from saturated alcohols, e.g.    methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate,    isopropyl(meth)acrylate, n-butyl(meth)acrylate,    sec-butyl(meth)acrylate, tert-butyl(meth)acrylate,    pentyl(meth)acrylate, hexyl(meth)acrylate, heptyl(meth)acrylate,    2-ethylhexyl(meth)acrylate, octyl(meth)acrylate,    nonyl(meth)acrylate, isooctyl(meth)acrylate, isononyl(meth)acrylate,    2-tert-butylheptyl(meth)acrylate, 3-iospropylheptyl(meth)acrylate,    decyl(meth)acrylate, undecyl(meth)acrylate,    5-methylundecyl(meth)acrylate, dodecyl(meth)acrylate,    2-methyldodecyl(meth)acrylate, tridecyl(meth)acrylate,    5-methyltridecyl(meth)acrylate, tetradecyl(meth)acrylate,    pentadecyl(meth)acrylate, hexadecyl(meth)acrylate,    2-methylhexadecyl(meth)acrylate, heptadecyl(meth)acrylate,    5-isopropylheptadecyl(meth)acrylate,    4-tert-butyloctadecyl(meth)acrylate, 5-ethyloctadecyl    (meth)acrylate, 3-isopropyloctadecyl(meth)acrylate,    octadecyl(meth)acrylate, nonadecyl(meth)acrylate,    eicosyl(meth)acrylate, cetyleicosyl(meth)acrylate,    stearyleicosyl(meth)acrylate, docosyl(meth)acrylate and/or    eicosyltetratriacontyl(meth)acrylate;-   cycloalkyl(meth)acrylate, such as cyclopentyl (meth)acrylate,    cyclohexyl(meth)acrylate, 3-vinyl-2-butylcyclohexyl(meth)acrylate    and bornyl(meth)acrylate; (meth)acrylates which derive from    unsaturated alcohols e.g. 2-propynyl(meth)acrylate,    allyl(meth)acrylate, and oleyl(meth)acrylate, vinyl(meth)acrylate;

The mixtures may, if appropriate, comprise

-   d) a monomer capable of free-radical polymerization and having at    least two terminal olefinic groups whose reactivity differs, for    example a bifunctional monomer having a methacrylate end group and a    vinyl end group, and/or-   e) at least one ethylenically unsaturated monomer (B), preferably    from the group of the methacrylates, particularly preferably    2-hydroxyethyl methacrylate.-   aminoalkyl(meth)acrylates, such as tris(2-methacryloxyethyl)amine,    N-methylformamidoethyl(meth)acrylate, 2-ureidoethyl(meth)acrylate;-   carbonyl-containing (meth)acrylates, such as    2-carboxyethyl(meth)acrylate, carboxymethyl(meth)acrylate,    oxazolidinylethyl(meth)acrylate, N-(methacryloyloxy)formamide,    acetonyl(meth)acrylate, N-methacryloylmorpholine,    N-methacryloyl-2-pyrrolidinone;-   (meth)acrylates of ether alcohols, e.g.    tetrahydrofurfuryl(meth)acrylate, vinyloxyethoxyethyl(meth)acrylate,    methoxyethoxyethyl(meth)acrylate, 1-butoxypropyl(meth)acrylate,    1-methyl-(2-vinyloxy)ethyl(meth)acrylate,    cyclohexyloxymethyl(meth)acrylate,    methoxymethoxyethyl(meth)acrylate, benzyloxymethyl(meth)acrylate,    furfuryl(meth)acrylate, 2-butoxyethyl(meth)acrylate,    2-ethoxyethoxymethyl(meth)acrylate, 2-ethoxyethyl(meth)acrylate,    allyloxymethyl(meth)acrylate, 1-ethoxybutyl(meth)acrylate,    methoxymethyl(meth)acrylate, 1-ethoxyethyl(meth)acrylate,    ethoxymethyl(meth)acrylate;-   (meth)acrylates of halogenated alcohols such as    2,3-dibromopropyl(meth)acrylate, 4-bromophenyl(meth)acrylate,    1,3-dichloro-2-propyl(meth)acrylate, 2-bromoethyl(meth)acrylate,    2-iodoethyl(meth)acrylate, chloromethyl(meth)acrylate;-   oxiranyl(meth)acrylates, such as 2,3-epoxybutyl (meth)acrylate,    3,4-epoxybutyl(meth)acrylate, glycidyl (meth)acrylate;-   amides of (meth)acrylic acid, e.g.    N-(3-dimethylaminopropyl)(meth)acrylamide,    N-(diethylphosphono)(meth)acrylamide,    1-(meth)acryloylamido-2-methyl-2-propanol,    N-(3-dibutylaminopropyl)(meth)acrylamide,    N-tert-butyl-N-(diethylphosphono)(meth)acrylamide,    N,N-bis(2-diethylaminoethyl)(meth)acrylamide,    4-(meth)acryloylamido-4-methyl-2-pentanol,    N-(methoxymethyl)(meth)acrylamide,    N-(2-hydroxyethyl)(meth)acrylamide, N-acetyl(meth)acrylamide,    N-(dimethylaminoethyl)(meth)acrylamide,    N-methyl-N-phenyl(meth)acrylamide, N,N-diethyl(meth)acrylamide,    N-methyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,    N-isopropyl(meth)acrylamide;-   heterocyclic (meth)acrylates, such as    2-(1-imidazolyl)ethyl(meth)acrylate,    2-(4-morpholinyl)ethyl(meth)acrylate and    1-(2-methacryloyloxyethyl)-2-pyrrolidone;-   phosphorus-, boron- and/or silicon-containing (meth)acrylates, such    as 2-(dimethylphosphato)propyl(meth)acrylate,    2-(ethylenephosphito)propyl(meth)acrylate,    dimethylphosphinomethyl(meth)acrylate,    dimethylphosphonoethyl(meth)acrylate,    diethyl(meth)acryloylphosphonate, dipropyl(meth)acryloyl phosphate;-   sulphur-containing (meth)acrylates, such as    ethylsulphinylethyl(meth)acrylate, 4-thiocyanatobutyl(meth)acrylate,    ethylsulphonylethyl(meth)acrylate, thiocyanatomethyl(meth)acrylate,    methylsulphinylmethyl(meth)acrylate, bis((meth)acryloyloxyethyl)    sulphide;-   bis(allyl carbonates), such as ethylene glycol bis(allyl carbonate),    1,4-butanediol bis(allyl carbonate), diethylene glycol bis(allyl    carbonate);-   vinyl halides, such as vinyl chloride, vinyl fluoride, vinylidene    chloride and vinylidene fluoride;-   vinyl esters, such as vinyl acetate.-   heterocyclic vinyl compounds, such as 2-vinylpyridine,    3-vinylpyridine, 2-methyl-5-vinylpyridine, 3-ethyl-4-vinylpyridine,    2,3-dimethyl-5-vinylpyridine, vinylpyrimidine, vinylpiperidine,    9-vinylcarbazole, 3-vinylcarbazole, 4-vinylcarbazole,    1-vinylimidazole, 2-methyl-1-vinylimidazole, N-vinylpyrrolidone,    2-vinylpyrrolidone, N-vinylpyrrolidine, 3-vinylpyrrolidine,    N-vinylcaprolactam, N-vinylbutyrolactam, vinyloxolane, vinylfuran,    vinylthiophene, vinylthiolane, vinylthiazoles and hydrogenated    vinylthiazoles, vinyloxazoles and hydrogenated vinyloxazoles;-   vinyl ethers and isoprenyl ethers;-   maleic acid and maleic acid derivatives, such as mono- and diesters    of maleic acid, the alcohol radicals having from 1 to 9 carbon    atoms, maleic anhydride, methylmaleic anhydride, maleimide,    methylmaleimide;-   fumaric acid and fumaric acid derivatives, such as mono- and    diesters of fumaric acid, the alcohol radicals having from 1 to 9    carbon atoms. for completeness, a di(meth)acrylate listed under    monomer (A) may also be used as monomer (B).

In this context, the term (meth)acrylates encompasses methacrylates andacrylates and also mixtures of the two. Correspondingly, the term(meth)acrylic acid encompasses methacrylic acid and acrylic acid andalso mixtures of the two.

The ethylenically unsaturated monomers may be used individually or inthe form of a mixture.

In principle, the composition of the inventive monomer mixtures may beas desired. It can be utilized to match the property profile of theinventive plastic to the demands of the application. However, it hasproven to be highly advantageous to select the composition of themonomer mixture in such a way that the prepolymer composed of thecompound(s) of the formula (I), (II) and (III) and the at least onemonomer (A) and styrene mix homogeneously at the desired polymerizationtemperature, because mixtures of this type are easy to handle due totheir generally low viscosity and, furthermore, can be polymerized togive homogeneous plastics with better properties.

According to one particularly preferred embodiment of the presentinvention, the monomer mixture comprises a prepolymer composed of atleast 5.0% by weight, preferably at least 20.0% by weight, particularlypreferably at least 50.0% by weight, of compounds of the formula (I),(II) and (III), based in each case on the total weight of the monomermixture. The proportion by weight of the monomer (A) is preferably atleast 2.0% by weight, preferably at least 10.0% by weight, particularlypreferably at least 20.0% by weight, based in each case on the totalweight of the monomer mixture. The proportion by weight of aromaticvinyl compounds, in particular styrene, is preferably at least 2.0% byweight, preferably at least 10.0% by weight, particularly preferably atleast 20.0% by weight, based in each case on the total weight of themonomer mixture.

According to one particular aspect of the present invention, the mixturecomprises

-   from 50 to 90% by weight, in particular from 60 to 85% by weight, of    the prepolymer of the monomers of the formulae (I) and/or (II) and    (III),-   from 2 to 50% by weight, in particular from 10 to 30% by weight, of    monomers (A), and from 2 to 50% by weight, in particular from 10 to    30%-   by weight, of aromatic vinyl compounds, in particular styrene, and-   from 0 to 45% by weight, in particular from 1 to 10% by weight, of    monomers of the formulae (XII) and (XIII), and/or monomers (B),    based in each case on the total weight of the monomer mixture.

The preparation of the monomer mixture to be used according to theinvention is obvious to the person skilled in the art. By way ofexample, it can take place via mixing of the prepolymer composed ofthio(meth)acrylates of the formulae (I) and/or (II) with (III), and ofthe aromatic vinyl compounds, and of the monomers (A) and (B), in amanner known per se.

For the purposes of the present invention, the monomer mixture ispreferably flowable at atmospheric pressure and temperatures in therange from 20.0 to 80.0° C. The term “flowable” is known to the personskilled in the art. It characterizes a liquid which can preferably becast into various shapes and, using suitable aids, stirred andhomogenized. For the purposes of the invention, particular flowablematerials have, in particular at 25° C. and at atmospheric pressure(101325 Pa) dynamic viscosities of the order of from 0.1 mPa·s to 10Pa·s, advantageously in the range from 0.65 mPa·s to 1 Pa·s. In oneparticularly preferred embodiment of the present invention, a castmonomer mixture has no bubbles, in particular no air bubbles. Preferenceis likewise given to monomer mixtures from which bubbles, in particularair bubbles, can be removed via suitable processes, such as temperatureincrease and/or application of vacuum.

The inventive high-transparency plastic is obtainable via free-radicalcopolymerization of the low-viscosity (η<200 mPa·s) monomer mixturedescribed above. Free-radical copolymerization is a well-known processinitiated via free radicals, converting a mixture of low-molecularmonomers into high-molecular-weight compounds, known as polymers. Forfurther details reference is made to the disclosure of H. G. Elias,Makromolekule [Macromolecules], Volume 1 and 2, Basle, Heidelberg, NewYork Hüthig und Wepf. 1990 und Ullmann's Encyclopedia of IndustrialChemistry, 5th edition, headword “Polymerization Processes”.

In one preferred embodiment of the present invention, the inventiveplastic is obtainable via mass or bulk polymerization of the monomermixture. Mass or bulk polymerization here means a polymerization processin which monomers are polymerized without solvent, the polymerizationreaction therefore being carried out on the undiluted material or inbulk. Processes which contrast with this are polymerization in emulsion(known as emulsion polymerization) and polymerization in a dispersion(known as suspension polymerization), in which the organic monomers aresuspended with protective colloids and/or stabilizers in an aqueousphase, and relatively coarse polymer particles are formed. A particularform of heterogeneous-phase polymerization is bead polymerization, whichin essence is a type of suspension polymerization.

In principle, the polymerization reaction may be initiated in any mannerfamiliar to the person skilled in the art, for example using afree-radial initiator (e.g. peroxide, azo compound) or via irradiationwith UV rays or with visible light, α-radiation, β-radiation orγ-radiation, or a combination of these.

In one preferred embodiment of the present invention, lipophilicfree-radical polymerization initiators are used to initiate thepolymerization. The free-radical polymerization initiators are inparticular lipophilic in order to dissolve in the bulk polymerizationmixture. Among compounds which may be used, besides the traditional azoinitiators, such as azoisobutyronitrile (AIBN) or1,1-azobiscyclohexanecarbonitrile, are aliphatic peroxy compounds, suchas tert-amyl peroxyneodecanoate, tert-amyl peroxypivalate, tert-butylperoxypivalate, tert-amyl 2-ethylperoxyhexanoate, tert-butyl2-ethylperoxyhexanoate, tert-amyl 3,5,5,-trimethylperoxyhexanoate, ethyl3,3-di(tert-amylperoxy)butyrate, tert-butyl perbenzoate, tert-butylhydroperoxide, decanoyl peroxide, lauryl peroxide, benzoyl peroxide andany desired mixtures of the compounds mentioned. Among theabovementioned compounds, very particular preference is given to AIBN.

In another preferred embodiment of the present invention, thepolymerization is initiated by using known photoinitiators, viairradiation with UV rays or the like. Use may be made here of thefamiliar, commercially available compounds, e.g. benzophenone,α,α-diethoxyacetophenone, 4,4-diethylaminobenzophenone,2,2-dimethoxy-2-phenylacetophenone, 4-isopropylphenyl 2-hydroxy-2-propylketone, 1-hydroxycyclohexyl phenyl ketone, isoamylp-dimethylaminobenzoate, methyl 4-dimethylaminobenzoate, methylo-benzoylbenzoate, benzoin, benzoin ethyl ether, benzoin isopropylether, benzoin isobutyl ether, 2-hydroxy-2-methyl-1-phenylpropan-1-one,2-isopropylthioxanthone, dibenzo-suberone,2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylphosphine oxideand other compounds, and the photoinitiators mentioned here may be usedalone or in a combination of two or more or in combination with one ofthe above polymerization initiators.

The amount of the free-radical generators may vary widely. By way ofexample, amounts preferably used are in the range from 0.1 to 5.0% byweight, based on the weight of the entire composition. Particularpreference is given to the use of amounts in the range from 0.1 to 2.0%by weight, in particular amounts in the range from 0.1 to 0.5% byweight, based in each case on the weight of the entire composition.

The polymerization temperature to be selected for the polymerization isobvious to the person skilled in the art. It is primarily determined viathe initiator selected and the manner of initiation (thermal, viairradiation, etc.). It is known that the polymerization temperature canaffect the properties of a polymer product. For the purposes of thepresent invention, preference is therefore given to polymerizationtemperatures in the range from 20.0 to 100.0° C., advantageously in therange from 20.0 to 80.0° C., in particular in the range from 20.0 to60.0° C. In one particularly preferred embodiment of the presentinvention, the reaction temperature is increased during the reaction,preferably in stages.

Heat-conditioning at an elevated temperature has also proven to beadvantageous, for example from 100 to 150° C., towards the end of thereaction.

The reaction may take place either at subatmospheric pressure or else atsuperatmospheric pressure. However, it is preferably carried out atatmospheric pressure. The reaction may take place in air or else underan inert gas, preferably with a minimum content of oxygen present,because this content has an inhibiting effect on any polymerization.

In one particularly preferred embodiment of the present invention, theprocedure for preparing the inventive high-transparency plastic preparesa homogeneous mixture from the components, these being monomer mixture,initiator and other additives, e.g. lubricants, and then charges thesebetween glass plates whose shape has been predetermined via thesubsequent application, e.g. in the form of spectacle lenses or otherlenses, prisms or other optical components. The bulk polymerization isinitiated via introduction of energy, for example via high-energyradiation, in particular using UV light, or via heating, advantageouslyin a water bath and for two or more hours. This gives the opticalmaterial in its desired form as clear, transparent, colourless, hardplastic.

For the purposes of the present invention, lubricants are additives forcharges of plastic materials, such as compression-moulding materials andinjection-moulding materials, their function being to increase the slipcapability of the materials charged and thus to ease the moulding of thecompression-moulding materials. Examples of substances suitable for thispurpose are metal soaps and siloxane combinations. The insolubility ofthe lubricant in plastics causes some of the lubricant to migrate to thesurface during processing, where it acts as a release agent.Particularly suitable lubricants, such as non-ionic fluorinated agentswith surface activity, non-ionic silicone agents with surface activity,quaternary alkylammonium salts and acidic phosphate esters, aredescribed in EP 271839 A, the disclosure of which is expresslyincorporated by reference for the purposes of the present invention.

The invention provides a high-transparency plastic with very goodoptical and mechanical properties. For example, its transmittance to DIN5036 is preferably greater than 88.0%, advantageously greater than89.0%.

The refractive index n_(D) of the inventive plastic is preferablygreater than or equal to 1.59. The refractive index of a medium isgenerally dependent on the wavelength of the incident radiation and onthe temperature. The inventive data for refractive index are thereforebased on the standard data specified in DIN 53491 (standard wavelengthof the (yellow) D line of sodium (about 589 nm)).

According to the invention, the Abbe number of the plastic ispreferably >36.0 to DIN 53491. Information concerning the Abbe numbercan be found by the person skilled in the art in the literature, forexample in the Lexikon der Physik [Dictionary of Physics] (WalterGreulich (ed.); Lexikon der Physik [Dictionary of Physics]; Heidelberg;Spektrum, Akademischer Verlag; Volume 1; 1998).

According to one particularly preferred embodiment of the presentinvention, the plastic has an Abbe number >36.0, advantageously >37.0,in particular >38.0.

The FDA falling ball test (ANSI Z 80.1) is used to test mechanicalproperties. The test is passed if the test specimen is undamaged by aball of diameter 16 mm. The greater the diameter of the ball used in thetest without damaging the specimen, the better the mechanicalproperties.

The inventive plastic also advantageously has a high glass transitiontemperature, and therefore maintains its outstanding mechanicalproperties, in particular its impact strength and its hardness, even attemperatures above room temperature. The glass transition temperature ofthe inventive plastic is preferably greater than 80° C., advantageouslygreater than 90° C., in particular greater than 95° C.

Possible fields of use for the inventive high-transparency plastic areobvious to the person skilled in the art. It is particularly suitablefor any application destined for transparent plastics. Itscharacteristic properties make it especially suitable for opticallenses, in particular for ophthalmic lenses.

The following inventive examples and the comparative example serve toillustrate the invention, with no intended resultant restriction.

EXAMPLES

Synthesis of the Thiomethacrylate Mixture

75.36 g of 1,2-ethanedithiol are weighed into an Erlenmeyer flask withinert gas feed and stirred, and 416.43 g of 13% strength NaOH solutionare metered in within a period of 30 minutes at from 25 to 30° C., withwater cooling. A brownish, clear solution forms.

178.64 g of methacrylic anhydride and the Na thiolate solution are thenmetered in parallel at the desired metering temperature within a periodof 45 minutes into the initial charge of stirred ethyl acetate/water inthe reaction flask. Where appropriate here, inert gas is passed over themixture. The contents of the flask generally become cooler by about 2°C. at the start of the feed, and a slightly exothermic reaction beginsafter about 5-10 minutes, meaning that appropriate cooling is applied inorder to maintain the desired reaction temperature (35° C.). Once thefeed has ended, the mixture is stirred for a further 5 minutes at 35° C.and is then cooled, with stirring, to about 25° C.

The mixture is transferred to a separating funnel and separated, and thelower, aqueous phase is discharged. For work-up, the organic phase istransferred to an Erlenmeyer flask and stirred with ®Dowex M-31 forabout 15 minutes, the ion exchanger then being filtered off.

The somewhat cloudy to almost clear crude ester solution is thenstabilized with 100 ppm of HQME and concentrated at not more than 50° C.on a rotary evaporator. The colourless final product is filtered at roomtemperature (20-25° C.). This gives about 140 g of colourless, clearester.

Preparation of prepolymer: reaction of 6.84 g of thethiodi(meth)acrylate and 0.36 g of DMDO in the presence of an amine ascatalyst, the method being based on EP 284374.

In an example of the preparation of a polymer based on an oligomericthiodimethacrylate, 7.2 g of the prepolymer, 2.4 g of styrene, 2.4 g ofdecaethoxylated bisphenol A di(meth)acrylate, 0.1 g of hydroxyethylmethacrylate, 36 mg of a UV initiator, e.g. Irgacur 819, and 24 mg oftert-butyl peroctoate or similar initiators (cf. Inventive Example 1)are mixed. The homogeneous casting resin mixture is placed in anappropriate mould and hardened within a period of 10 min in a UV curingsystem using a 1200 W high-pressure mercury source. The material is thenheat-conditioned for a further period of about 2 h at about 120° C. inan oven.

Average Refractive/ FDA ball Abbe falling diameter coefficient DIN balltest in mm, 53491 diameter test Experiment System 589 nm OdourTransmittance ANSI Z80.1 passed Inventive PLEX 6931/DMDO prepolymer co1.5939 38.2 no 89 passed 18 Examples styrene co E10BADMA = 60:20:20 IE 1plus 1% HEMA Comparative Examples CE I PLEX 6931 co DMDO co styrene co —— yes — — — E10BADMA = 57:3:20:20 plus 1% HEMA (#) CE II PLEX 6931 costyrene co E10BADMA = 60:20:20 1.5959 34.9 no 89 passed 16 plus 1% HEMACE III PLEX 6931/DMDO prepolymer co 1.6089 29.6 no 89 passed 16 styrene= 70:30 plus 1% HEMA Plex 6931 O: reaction product from methacrylicanhydride and ethanedithiol from DE 316671 E10BADMA: ethoxylatedbisphenol A dimethacrylate, degree of ethoxylation about 10 DMDO:dimercaptodioxaoctane HEMA: hydroxyethylmethacrylate (#): no furtheranalysis was undertaken, because of the problems of odour.

The inventive mixture (IE 1) is odourless. The Comparative Example CE Idid not pass this test and was therefore not studied further.

For comparable refractive index (of IE 1 with CE II and CE III) the Abbenumber was nevertheless better for the inventive mixture. The inventivemixture also performed substantially better in the falling ball test.

1. A mixture for preparing a transparent plastic, comprising: a) aprepolymer prepared from compounds of the formula (I) and (II) and fromalkyl dithiols or from polythiols

wherein each R¹ is hydrogen or a methyl radical, each R² is a linear orbranched, aliphatic or cycloaliphatic radical, or a substituted orunsubstituted aromatic or heteroaromatic radical, and each of m and n,is a whole number greater than or equal to 0, wherein m+n>0, and b) atleast one monomer (A) capable of free-radical polymerization and havingat least two methacrylate groups, and c) aromatic vinyl compounds, andd) a monomer selected from the group consisting of a monomer capable offree-radical polymerization and having at least two terminal olefinicgroups whose reactivity differs, e) at least one ethylenicallyunsaturated monomer (B) and mixtures thereof; and f) a monomer capableof free-radical polymerization and having at least two terminal olefinicgroups whose reactivity differs, of the formula (XIVa)

wherein s and t are greater than or equal to zero and the sum s+t is inthe range from 1 to
 20. 2. The mixture according to claim 1, comprisingmore than 10 mol %, of compounds of the formula (II) wherein m+n=2,based on a total amount of the compounds of the formula (I), (II) andcompounds obtained from alkyl dithiols or from polythiols.
 3. Themixture according to claim 1, wherein the radical R² of the formulae (I)and/or (II) is an aliphatic radical having from 1 to 10 carbon atoms. 4.The mixture according to claim 1, comprising more than 5.8 mol % ofcompounds of the formula (II) wherein m+n=3, based on a total amount ofthe compounds of the formula (I) and (II) and compounds obtained fromalkyl dithiols or from polythiols.
 5. The mixture according to claim 1,comprising from 0.1 to 50 mol % of compounds of the formula (I), basedon a total amount of the compounds of the formula (I), (II) andcompounds obtained from alkyl dithiols or from polythiols of compoundsof the formula (I).
 6. The mixture according to claim 1, comprising from1 to 40 mol % of compounds of the formula (II) wherein m+n=1, based on atotal amount of the compounds of the formula (I), (II) and compoundsobtained from alkyl dithiols or from polythiols.
 7. The mixtureaccording to claim 1, comprising compounds of the formula (IL) whereinm+n>3.
 8. The mixture according to claim 1, wherein the total content ofcompounds of the formula (I), (II), and (I), (II) and compounds obtainedfrom alkyl dithiols or from polythiols is at least 5.0% by weight, basedon the total weight of the mixture.
 9. The mixture according to claim 1,wherein the mixture comprises at least one monomer (A) which iscopolymerizable with the prepolymers prepared from the monomers offormulas (I), (II) and compounds obtained from alkyl dithiols or frompolythiols.
 10. The mixture according to claim 9, wherein the mixturefurther comprises di(meth)acrylates.
 11. The mixture according to claim1, wherein the aromatic vinyl compounds comprise styrene.
 12. Themixture according to claim 1, comprising allyl polyethylene glycolmethacrylate.
 13. The mixture according to claim 1, wherein (B)comprises 2-hydroxyethyl methacrylate.
 14. A process for preparing atransparent plastic, comprising: polymerizing the mixture of claim 1.15. A transparent plastic prepared by the process of claim
 14. 16. Theplastic according to claim 15, having a refractive index of the plasticto DIN 53491 is greater than 1.59.
 17. The plastic according to claim15, having a Abbe number of the plastic to DIN 53491 is greater than 36.18. The plastic according to claim 15, wherein an average diameter of aball which does not damage the test specimen in a falling ball testis >18.
 19. The plastic according to claim 15, having a transmittance ofthe plastic to DIN 5036 is ≧89%.
 20. The plastic according to claim 15,having a glass transition temperature is greater than 80.0°C.
 21. Amethod of using a high-transparency plastic, comprising: forming thehigh-transparency plastic according to claim 15, into an optical lens.22. An optical lens, comprising: the transparent plastic according toclaim
 15. 23. A mixture for preparing a transparent plastic, comprising:a) a prepolymer prepared from compounds of the formula (I) and (II) andfrom alkyl dithiols or from polythiols.

wherein each R¹ is hydrogen or a methyl radical, each R² is a linear orbranched, aliphatic or cycloaliphatic radical, or a substituted orunsubstituted aromatic or heteroaromatic radical, and each of m and n,is a whole number greater than or equal to 0, wherein m+n>0, and b) atleast one monomer (A) capable of free-radical polymerization and havingat least two methacrylate groups, and c) aromatic vinyl compounds, andd) a monomer selected from the group consisting of a monomer capable offree-radical polymerization and having at least two terminal olefinicgroups whose reactivity differs, e) at least one ethylenicallyunsaturated monomer (B) and mixtures thereof; and f) a monomer mixturecapable of free-radical polymerization and having at least two terminalolefinic groups whose reactivity differs, which is a mixture of amonomer of formula (XIII) and a monomer of formula (XIVa):

wherein the residues R²³ and R²⁴ each independently of each other are ahydrogen or a methyl residue, and the residue R²⁵ designates a linear orbranched, aliphatic or cycloaliphatic divalent residue or a substitutedor unsubstituted aromatic or heteroaromatic divalent residue, p and qare independently from 1 to 40; and

wherein s and t are greater than or equal to zero and the sum s+t is inthe range from 1 to 20.